Gasification of coal



Jan. 17, 1,967 T. T. GRAHAM GASIFICATION OF COAL Filed May 27. 1964 4 Sheets-Sheet 1 vm Sw w NSS 7720/770.: 7.' Gra/50m INVENTOR.

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' GASIFICATION oF COAL ATTO/PA/EVJ United States Patent() 3,298,434 GASIFICATION F COAL Thomas T. Graham, 2431 Shakespeare, Houston, Tex. 70025 Filed May 27, 1964, Ser. No. 370,606 6 Claims.l (Ci. 1662) This invention relates to a process for the gasicationof coal in situ.

Coal is frequently burned under cont-rolled conditions to gasify the volatile matter and to manufacture producer gas, synthesis gas, etc. It would be advantageous to be able to burn the coal in situ to obtain these volatiles and gases, but up until this time no practical eco-nomic method has ybeen available for burning the coal in situ.

It is an object of this invention to provide a method of burning coal in situ to obtain the tars, oils, fuel gases, etc. available when coal is burned under controlled conditions.

Another object is to provide ya method of burning coal in situ wherein a constant check is kept of temperature conditions to permit burning the-coal under controlled conditions. f i

Another object is to provide a method of burning' coal in situ in which the burning is carried out at selected temperature levels. e l

Another object is to provide a method of `burning coal in situ using steam'and air injected into the coal seam in which the injection well is kept free of condensate so that the hot steam and air can freely reach the ame front.

Other objects, features and advantages of the invention will be apparent from the drawings, specification and the claims.

In the drawings, wherein like reference numerals indicate like parts, and wherein the methods of this invenf tion are depicted:

FIGURE 1 is a schematic view of surface equipment used in practicing this invention; v

FIGURE 2 illustrates one process .in accordance with this invention; A

FIGURE 3 illustrates one process in accordance with this invention;

FIGURE 4 illustrates another process in accordance with this invention; y

FIGURES 5a, 5b and 5c are schematic views showing a well penetrating Va coal seam and illustrating in successive stages refluxin-g of the injection well in accordance with `this invention; and j FIGURE 6 is a chart of pressure and time illustrating these values during refluxing.

In practicing this invention, a well is first sunk to the coal seam. As substantial pressures are to be used, a seam should be selected'where a suitable cap `and overburden will con-tain the pressure. In one form of the invention, the fluids are injected and the lgases recovered from the same injection well. In other -forms of the in- Vention, production wells are drilled into the coal seam. Where production wells are drilled, channels of communication are provided between the injection an-d production wells in any desired manner to permit flow of gases between the wells. It is well known that this may be done `by mining, by hydrofracing, or electrolinking-carbonization.

Air and stream are then injected through the injection well and the coal ignited. In some forms of the mehod the air and steam are injected as a mixture, and in others they are injected alternately. The time of injection` of the alternate air and steam land the ratio of air to steam in mixed injection controls the temperature at the flame front. Of course, as soon as injection is commenced, the formation is set on re in any well known manner. For instance, the use of a sufficiently hot injection fluid will "ice ignite the coal seam. Many other well known means of i gniting the seam may be practiced.

As the flame front moves away from the well, the heat at the Well decreases and condensates collect in the well. By this invention these condensates are periodically removed from the well so that they do not interfere with the injection of air and steam. At the time that these condensates are removed from the well, fluids from j the vicinity of the flame front are also returned to the surface and their condition ascertained so that the temperature at the ame front will be known. Their condition may be readily determined by measuring the temperature of the fluids or by analyzing thefluids to determine the content of carbon monoxide andlcarbon dioxide. Either or both methods may be used under varying circumstances. According to the temperature found to exist, the time of injection of alternate air and steam or the r-atio of air and steam when injected in a mixture may be varied to maintain the desired temperature at the flame front.

VAt a relatively low temperature from below around l200 F. most if not all of the volatile products will be volatilized.

Where air and water vapor are present, burning of coal will result in a carbon dioxide and hydrogen product if the temperature is below 1832 F. Above l832 F. a fuel mixture of, carbon monoxide and hydrogen will be produced. Where steam is not present, the burning of coal below 1832.e F. will give a ,relatively inert carbon monoxide and nitrogen product.

From the above it is obvious that the volatiles can be obtained at a lower temperature, but they would thus be obtained in the absence of a usable fuel gas. The coal must be burned at about 1832 F. to givea fuel gas. The higher the temperature above this point, the more carbon gasied, and hence the more fuel gas. However, normal iron equipment can only withstand around 2600o F., and if the coal is to beburned -at -a temperature such that the equipment in the bottom of the well will be exposed to more than 260051:., then special heat-resistant equipment should be used.

By utilizing this process, fuel gas made up principally of carbon monoxide and hydrogen may be recovered. Also, there will be recovered the light oil products benzene, toluene, xylene and naphtha. The gas chemicals ammonium sulfate, cyanide chemicals and sulphur will also be recovered. Also the tar chemicals naphthalene, the .tar acids and tar bases will be recovered.

Referring to FIGURE 1, water is obtained from a suitable water well 10 and purified in lter 11 and water treater 12. The purified water is stored for use in tank 13. As needed the water is withdrawn from tank 13 by the metering pumps 14 and 15 and delivered to the heater 16. The heater 16 may be the conventional gas- -red type with fuel obtained from a storage tank 17.

Air `compressor 18 maintains a supply of air under pressure in air tank 19. This air is .metered as needed by valve 2,1 and delivered to the heaters 16. The pressure and temperature of the air leaving the tank may be recorded by the pressure-sensitive instrument 22 and the temperature-sensitive instrument 23. The air is heated in the heater 16 and combined with the steam. The combined air and steam is then delivered through line 24 to the injection Well casing 25. Normally the steam-air mixture will be introduced into the casing 25 through branch line 24a, but, if desired, it may pass through branch line 24b to the tubing.

Also,it is apparent that the system just explained may be utilized to alternately inject air and steam -by suitable control of the air tank valve 21 and the water metering pumps 14 and 15.

A suitable temperature control device 27 is sensitive to the temperature in line 24 and controls the flow of fuel from tank 17 to heater 16 to permit maintaining of a desired temperature in line 24.

After injection of air or air and steam is begun, the well may be set on fire either due to the heat of the injected fluids or by a special formation-lighting device. As there are no fuel gases available until after the formation is on fire, it is not necessary to initially inject steam, and only air will normally be used. A mixture of air and steam could be used if desired.

After the formation is on re, air and steam are injected as a mixture, or alternatively, depending on the method used.

In accordance with this invention, the well is now periodically reiluxed to reflux the formation and to remove from the well condensates which may have collected therein. For this purpose, the outlet line 28 from tubing 26 is provided with a quick-opening valve 29. The valve 29 may be controlled by a suitable timer 31. As the v'alve 29 opens, the pressure in the well forces the liquids above the level of the tubing 26 up through the tubing to the surface and -out-line 28. As these fluids leave the well, their temperature may be determined -by instrument 32 and, if desired, gas analyzer 33 may be utilized to determine the condition of the reflux gases. From line 28 the reflux gases pass to the separator 34 and liquids sepa- -rated out pass to storage tank 35. Gases pass olf through line 36.

Reference is made to FIGURES a through 5c wherein the reilux action on the coal seam is depicted. In FIG- URE Sa the condition is depicted in which the injection well is under a pressure of 1,000 p.s.i. Fluids are being injected through line 24a. This will result in a pressure in the bottom of the hole of around 950 pounds. This pressure will reduce progressively away from the well.

It is noted that the bottom of the tubing 26 extends down` to at least the level of the coalseam and preferably extends to approximately the bottom of the coal seam. Thus as liquids 37 accumulate, they rise above the bottom of the tubing 26.

FIGURE 5b shows the cleaning of the Well and reiluxing of the coal seam when the valve 29 in the tubing is open. The accumulated pressure within the well, assisted by the pressure continuously being injected through inlet line 24a, drives the liquids accumulated above the lower end of the tubing up through the tubing to the surface. After the reiluxing action, the well will be in the condition shown in FIGURE` Scin which liquids have been cleaned out and the coal seam is open and free to receive lluids thereafter being injected.

FIGURE 6 depicts the periodic reluxing and the change in pressures which occur as represented by line 37. It will be noted that when the valve is open, the pressure drops fairly rapidly to about 800 p.s.i.; when the valve is closed, it again rises fairly rapidly to the 1000-pound injection pressure. As depicted,` the well is relluxed for only a short period of time.

While the illustrated embodiment employs an injection pressure of 1000 pounds, it will be appreciated that other injection pressures may be used, depending upon the circumstances encountered in the particular coal seam.

Where the system includes one or more production wells, the coal seam will rst be fractured as hereinabove discussed to provide channels between the injection well and the production Well. As shown in FIGURE 1, the production well may include a casing 38 with a tubing 39 therein. Preferably the tubing 39 will extend down to the bottom of the coal seam. As the gases from the burning coal reach the production well, they will normally rise up the tubing 39 and pass out through line 41 to the separator 42. At the surface the volatiles will liquefy and be separated out in separator 42 and pass to the storage tank 43. Fuel gas is taken olf of separator 42 through line 44a and Sent to distribution.

In the event the production well is a sufficient distance from the flame front, the gases may cool suiliciently in the production Well to result in condensate collecting in the bottom of the well. Condensate may also form before the gases reach the well. To raise this liquid to the surface, a portion of the gas from separator 42 is stored in tank 40 and is returned to the well by compressor 44 through line 45. This compressed gas is introduced into the casing and gas lifts the liquid in the bottom of the production well through the tubing.

A suitable temperature instrument 46 records the temperature of the fluids leaving the production Well and a gas analyzer 47 may be utilized to determine the composition of the gas. This temperature and composition information may be correleated fwith that obtained from the rellux -on the injection well to determine the temperature at the flame front. Obviously, if fuel gas is desired and carbon dioxide is shown to be present in large volume by the gas analyzers, the temperature in the well would be permitted to rise by reducing the amount of steam introduced, as it would be known that the flame front was burning at a temperature less than 1832 F. On the other hand', if the temperature indicators show an elevated temperatur, say 2700 or 2800 F., and the llame front is fairly close to eitiher the injection or production well, that must be taken that the temperature is now greater than the equipment in the well will withstand, and the amount of steam might be :increased to reduce the temperature at the llame front. Of course, where special heat-resistant materials are used, the temperaturernight be permitted to go much higher.

Reference is now made to FIGURE 2 wherein a system is depicted which utilizes the injection well only. As shown, the .operation of this system begins after the formation is on tire and ready to produce. The cycle has a low temperature of` around 1600 to 1700 F. at the surface, as this would reflect a temperature of around 1832" F. at the llame front. Of course, as the llame front moves away from the we'll, these surface temperatures would reduce. As shown -by the graph line 48, air is injected through the injection well until such time as the rellux lluifds from the well indicate that t-he llame front temperature is a substantial value above 1832 F. Depending upon the installation, this may vary from about 2200" F. to 2600 F. Where special heat-resistant equipment is used, the temperature might be greater. In any event, it is a substantial value above l832 F. so that a substantial amount of steam will be necessary to reduce the temperature at the flame front back to 1832 F. because the passing Vof steam over the hot coal will result in manufacturing of fuel gas consisting primarily of carbon monoxide and hydrogen. Also, the volatiles of the coal will be volatilized as the flame front moves back in the coal seam and these volatiles will be recovered. During this stage of the proceeding, steam is injected and fuel gas is refluxe'd out of the injection well. The periodic introduction of steam and `alternate reiluxing may be carried out at such time intervals as are appropriate for the best efliciency. This introduction of steam and reiluxing of fuel gas is indicated by the line 48a. The ya1- ternate introduction of steam and relluxing of fuel gas is continued until the temperature at the llame front reduces to about 1832 F. This twill be apparent from the reduction in temperature of the reflux at the surface, and the operator will be able to approximate the temperature at which he should return to the air injection cycle to reheat the coal. Of Course, the gas analyzer would be the most sensitive means of determining when the formation temperature falls below 1832 F., as the production of carbon monoxide begins to give way to the production of carbon dioxide. As shown, the cycle is continuously repeated in the manner explained, with fuel gas and volati'les being recovered during the lsteam cycle, and with volatiles being recovered during the air cycle and the inert gas released to atmosphere.

In FIGURE 3, an alternate method of operation is shown in which the production well is used to recover the gases. Air is first introduced and 'the `formation set on `fire as depicted by line 49. As the temperature rises, the volatiles are gasifed and are pushed on toward the production well due to the pressure of the fluids being introduced. Of course, the well would have been treated to provide channels through which the gas may pass to the production well. After the llame front cornes up to a temperature above l832 F., las possibly indicated by a surface temperature of 1900 to 2000 F., the burning coal will produce 'a fuel gas of carbon monoxide and hydrogen, as depicted by line 49a. During periodic relluxing of the well, any condensate in the injection well will be recovered and the temperature in the llame front will be held at the desired level by varying the proportions of the air and steam injected as called for by the temperature indicator 32 and the gas `analyzer '33. In accordance with this form of the invention, the formation-between the injection and production well is made to. burn at a temperature slightly greater than l832 F. until the flame front reaches the production well. At ythis time, the burned coal is still capable of generating additional fuel gas if burned at a higher temperature, and the formation may be reburned atr very high temperatures, say 3000 to 3400 F., to produce this gas as indicated by line 49h. At this time the production Well may be utilized as the injection welll and the injection well as the production well, land the flame front forced to move back towards the injection well. The steam injected in the injection well will normally keep the injection well temperature down. Where the equipment in the production well will not withstand the high temperature, additional steam may be injected into the production wellto hold its temperature down to a permissible level.

FIGURE 4 shows a still further method of practicing this invention. Again air is injected as indicated by lline 51 and the formation set on lire. The coal seam is brought up to the maximum temperature at which it is to be maintained. For instance, this may -be 2500 to 2600 F. Utilizing the principle of reflux and controlling the temperature a-s explained hereinabove, the coal seam will be forced to burn at this selected temperature from the injection well to the production Iwell. During this time, the volatiles of tar and the fuel gas produced will be recovered through the production well as indicated by line 51a.

From the above explanation of three illustrative meth- -ods in accordance with this invention, it is 4apparent that the coal seam may be burned in situ in any desired manner and the flame f-ront temperature controlled -by relluxing the injection well to determine the temperature and then varying the ratio or time of injection of air and steam to obtain the desired temperature. It is this principle of relluxing and control in accordance with the condition of the rellux lluids which characterizes this inventio-n and makes it possible to control the in situ burning of coal.

Any desired equipment may be used in practicing the method. However, the injection tubing should extend down to the coal seam and preferably to the bottom of the coal seam so that condensates, and particularly water, condensed in the well can be removed. While it is desirable to have steam present at the flame front, it is not desirable to have slugs of water present. Steam in small amounts will decompose in a controlled manner to provide oxygen for combining with the carbon. Where slugs of water are present, they would tend to blanket a section of the llame front and interfere with this action.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and various changes in the method may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A method of recovering gases from a coal seam into which a well bore extends, said bore having a tubing 6 therein lextendir'ig down to at least the coal sarn comprising,

injecting air into said coal, l igniting ythe coal and continuing the air injection until the temperature of the burning coal is substantially in excess of l832 F., f

periodically opening said tubing `at the surface during the air injection period to rellux the coal seam and remove from the well bore liquids which may have .accumulated therein and the gaseous products of combustion from said coal seam,

determining the temperature in the coal seam by determining the condition of the reflux lluids, then upon thefburning coal reaching the desired temperature stopping the injection of air and injecting steam,

periodically opening said tubing at the surface during the steam injection period to reflux the coal seam and remove from the welll bore any liquids which may have accumulated therein and the gaseous products ofcombustion from said coal seam,

determining the ltemperature in the coal seam by determining the condition of said last mentioned reflux fluids,

repeating the air injection cycle after the temperature ofthe burning coal has been reduced to about 1832 F.,

and thereafter repeating the alternate air and steam injection steps. Y

2. A method of recovering gases from a coal seam into which a well bore extends, said bore having a tubing therein extending down to at least the coal seam comprising, f

injecting air into said coal,

igniting the coal,

thereafter injecting air and steam into the coal,

periodically opening said tubing at the surface to rellux the coal seam and remove from the well bore liquids which may have accumulated therein, determining the temperature in the coal seam by determining the condition of the reflux lluids, controlling the injection of steam and air as required by the condition of the rellux lluids to obtain selected temperature conditions in the Well,

and recovering the gaseous products of combustion from said coal seam.

3. A method of recovering gases from a coal seam into which a plurality of well bores extend, at least one of said bores having a tubing therein extending down to at least the coal seam and providing an injection well, said other bore providing a production well, comprising injecting air into the injection Well,

igniting the coal and continuing the air injection until the coal reaches a temperature of 1832 F., thereafter injecting a mixture of air and steam into the injection well, periodically -opening said tubing at the surface to rellux the c'oal seam and remove from the injection Well bore liquids which may have accumulated therein,

determining the temperature in the coal seam by determining the condition of the rellux fluids,

controlling the temperature of the burningv coal by varying the ratio of steam and air injected to burn the coal at a temperature below 1832" F. but above the temperature at which all of the volatiles of the coal are gasied,

then burning the coal at a temperature slightly above 1832 F. to make carbon monoxide gas,

then burning the coal at a temperature over 3000 F.

to make additional gas,

and recovering said gases from the production well.

4. A method of recovering gases from a coal seam into which a plurality of well bores extend, at least one of said bores having a tubing therein extending down to at least the coal seam and providing an injection well,

said other bore providing a production well, comprising,

injecting air into the injection Well,

igniting the coal and continuing the air injection until the coal reaches a temperature of 1832" F.,

thereafter injecting a mixture of air and steam into the injection Well,

periodically opening said tubing at the surface to reflux the coal seam and remove from the injection Well bore liquids which may have accumulated therein,

determining the temperature in the coal seam by determining the condition of the reux fluid,

controlling the temperature of the burn-ing coal by Varying the ratio of steam and air injected to burn the coal at a temperature above 1832 F. but below 6. A method of recovering gases from a coal seam into which a plurality of well bores extend, at least one of said bores having a tubing therein extending down to at least the coal seam and providing an injection Well, said other bore providing a production well, comprising,

injecting air into said coal,

igniting said coal,

thereafter injecting air and steam into the coal,

periodically opening said tubing at the surface to reflux the coal seam and remove from the vyell bore fluids which may have accumulated therein, recovering the gaseous fluids resulting from combustion of said coal through said production well, determining the temperature in the coal seam by deabout 2600 F., l5 termining the condition of one of said iluids from and recovering the gases from the burning coal from the injection and production Wells,

the production well. l controlling the injection of steam and air as required 5. A method of recovering gases from a coal seam by the temperature in the coal seam to obtain seinto which a plurality of well bores extend, at least one lected temperature conditions in the well, of said bores having a tubing therein extending down 20 and controlling the temperature in the production Well to at least the coal seam and providing an injection well, independently ofthe temperature of the burning coal. salijgltigbeir;ofroducnon Wen Compnsmg References Cited by the Examiner igniting said coal, UNITED STATES PATENTS thereafter injecting air and steam into the coal, 25 2,695,163 11/1954 Pearce et 1 166 11 periodically opening said tubing at the surface to re- 2,788,956 4/1957 Pevere et aL 166 11 flux the C031 Seam and remove from the well bore 2,795,279 6/1957 Sarapuu 166 11 fluids which may have accumulated therein, 2,841,375 7 /1958 Salomonsson 166 11 X recovering the gaseous fluids resulting from combustion `3,004,595 10/1961 Crawford et a1, 166 11 0f Said C0211 through Said production well, 30 3,013,609 12/1961 Ten Brink 166-11 X determining the temperature in the coal seam by dey3,032,102 5/1962 parker 166 11 termining .the condition of one of said uids from 3,136,359 6/1964 Graham 166-40 X the injection and production wells, 3,240,270 3 /1966 MarrX 166 11 X and controlling the injection of steam and air as re-v quired by the temperature in the coal seam to obtain selected temperature conditions in the well.

35 CHARLES E. OCONNELL, Primary Examiner.

S. J, NOVOSAD, Assistant Examiner'. 

2. A METHOD OF RECOVERING GASES FROM A COAL SEAM INTO WHICH A WELL BORE EXTENDS, SAID BORE HAVING A TUBING THEREIN EXTENDING DOWN TO AT LEST THE COAL SEAM COMPRISING, INJECTING AIR INTO SAID COAL, IGNITING THE COAL, THEREAFTER INJECTING AIR AND STEAM INTO THE COAL, PERIODICALLY OPENING SAID TUBING AT THE SURFACE TO REFLUX THE COAL SEAM AND REMOVE FROM THE WELL BORE LIQUIDS WHICH MAY HAVE ACCUMULATED THEREIN, DETERMINING THE TEMPERATURE IN THE COAL SEAM BY DETERMINING THE CONDITION OF THE RELFUX FLUIDS, CONTROLLING THE INJECTION OF STEAM AND AIR AS REQUIRED BY THE CONDITION OF THE REFLUX FLUIDS TO OBTAIN SELECTED TEMPERATURE CONDITIONS IN THE WELL, AND RECOVERING THE GASEOUS PRODUCTS OF COMBUSTION FROM SAID COAL SEAM. 